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Verifying files are copied correctly from a disk image

After you use a disk image to restore a disk or burn a CD or DVD, you can use checksums to verify that the files were copied correctly. A checksum is a calculation of all the data on a disk or disk image that yields a specific number.

You can compare this number with the checksum of the source image. If the two numbers are the same, the files were copied exactly.

  1. In Disk Utility, select the source disk image in the list.
  2. Choose Images > Checksum, then choose either “CRC-32 image checksum” or “MD-5 image checksum.” Most disk images store data using a CRC32 checksum. A few store an MD-5 checksum.

    The checksum appears in the progress message and looks similar to "CRC32 $D1BDA609."

  3. Select the restored disk or the CD or DVD your burned, and checksum it.
  4. Compare the two number to verify that they match.

You can also find the checksum in the Disk Utility log. To see the log, choose Window > Show Log.

The checksum of a disk or disk image changes when you add or delete files. For the most reliable results, use disk images that are formatted read-only.

See also

disk images